1. Field of the Invention
This invention relates to an improved elastomeric composition of metal neutralized sulfonated elastomeric polymers which are plasticized with critically selected polydentate amines wherein the plasticized compositions have improved rheological properties. These elastomeric compositions can be processed on conventional plastic fabrication equipment into high performance elastomeric articles.
2. Description of the Prior Art
Recently a new class of thermoelastic sulfonated polymers has been described in a number of U.S. patents. These sulfonated polymers are derived from polymeric materials having olefinic unsaturation, especially elastomeric polymers such as Butyl and EPDM rubbers. U.S. Pat. No. 3,642,728 herein incorporated by reference, clearly teaches a method of selective sulfonation of olefinic unsaturation sites of an elastomeric polymer to form an acid form of a sulfonated elastomeric polymer. The olefinic sites of the elastomeric polymer are sulfonated by means of a complex of a sulfur trioxide donor and a Lewis base. The SO.sub.3 H groups of the sulfonated elastomer can be readily neutralized with a basic material to form an ionically crosslinked elastomer having substantially improved physical properties over an unsulfonated elastomer at room temperature. However, these ionically crosslinked elastomers may be processed like a conventional thermoplastic at elevated temperatures under a shear force in the presence of selected preferential plasticizers which dissipate the ionic associations at the elevated temperatures thereby creating a reprocessable elastomer.
The basic materials used as neutralizing agents are basic materials selected from Groups I, II, III, IV, V, VIB, VIIB and VIII and mixtures thereof of the Periodic Table of Elements. Although these sulfonated elastomeric polymers prepared by the process of U.S. Pat. No. 3,642,728 are readily usable in a certain number of limited applications, they are not as readily adaptable for the manufacture of an injection moldable elastomeric article such as footwear as are the improved compositions of the present invention, wherein improved rheological properties are realized.
U.S. Pat. No. 3,836,511, herein incorporated by reference, teaches an improved process for the sulfonation of the olefinic sites of the elastomeric polymer, wherein the improved sulfonating agent is selected from acetyl sulfate, propionyl sulfate and butyryl sulfate. The neutralizing agents employed to neutralize the acid form of the sulfonated elastomeric polymers are organic amines. The improved compositions of the present invention are neutralized with inorganic counterions.
U.S. Pat. No. 3,870,841, herein incorporated by reference, teaches a method of plasticization of the polymeric backbone of a neutralized sulfonated plastic polymer by means of a polymer chain plasticizer which is a liquid compound having a boiling point of at least about 120.degree. C. The polymer chain plasticizer is selected from a dialkyl phthalate, a process oil or an organic acid ester. Additionally, a domain plasticizer can be incorporated into the composition, wherein the domain plasticizer reversibly disrupts the association of the sulfonate groups at a temperature of forming. The compositions of this patent are based on plastic backbones, whereas compositions of the present invention are based on elastomeric backbones. The compositions formed by the process of U.S. Pat. No. 3,870,841 are not as suitable for the manufacture of high performance elastomeric articles such as elastomeric tubing formed by an extrusion process as are the compositions of the present invention.
U.S. Pat. No. 3,847,854, teaches a method of improving the processability of neutralized sulfonated elastomeric polymers by the addition of a preferential plasticizer which has at least one functional constituent which exhibits a bond moment whose absolute value is at least 0.6 Debyes, and must be a liquid at the desired processing temperature of the neutralized sulfonated elastomeric polymer. However, the plasticizers falling within this criterion exhibit a very large range in plasticizing effectiveness so this criterion gives no help in choosing which chemicals will be most effective in improving processability of the sulfonated polymer. This invention fails to teach the use of the critically selected polydentate amines of the instant invention as plasticizers. The inventive concept of the present instant invention clearly teaches the use of certain critically selected polydentate amines as preferential plasticizers in order to achieve improved rheological properties. Furthermore, these selected polydentate amines do not fall into the classes taught in U.S. Pat. No. 3,847,854; they are not volatile plasticizers since they substantially remain in the polymer after fabrication, and they are not non-volatile plasticizers as taught by this patent because they are liquids over the use temperature range.